For some types of inkjet printer ink cartridges ink is introduced into the cartridge through one or more fill holes molded into the cartridge housing. Ink fill holes are often positioned at the top of the cartridge so that the holes may also function as vent holes for venting the ink holding chamber(s) within the housing. In one such ink cartridge, a “vent plug” is inserted into each fill hole after the cartridge is filled with ink. The vent plug substantially closes the fill hole, leaving just a small opening or gap for venting the ink chamber. Ink fill holes are typically quite small, about 1/10 inch in diameter in some cartridges, and the vent openings are significantly smaller. Accordingly, the vent plugs are also very small. Fabricating and installing the tiny vent plugs adds significantly to the cost of the ink cartridge. Also, problems are sometimes encountered fabricating and installing vent plugs due to the small size of the plugs. For example, particulate debris and deformed plugs can jam or otherwise disable the automated machinery used to make and install the plugs, causing costly downtime and repairs.